To investigate the mechanism of wall heat loss in diesel engines, high-speed imaging of infrared thermal radiation from the chromium-coated quartz wall surface impinged by a diesel spray flame has been explored by the authors using a high-speed infrared camera at 10 kHz frame rate and 128×128 pixel resolution. This method successfully achieved experimental separation and visualization of radiative and convective heat transfer components using a MgF2 window. The convective heat flux exhibited radially striped patterns and these stipes were not observed in radiative heat flux distribution. Radiative heat transfer contribution might be greater than previously reported, particularly during the early stages of flame–wall interaction. Furthermore, to explore the potential of structured wall surfaces for reducing cooling losses, comparative experiments were conducted using circular and teardrop-shaped dimple structures on the wall. In the case of circular dimples, while the upstream inside the dimples exhibited lower wall temperatures due to flow separation, significantly higher temperatures were observed downstream because of vortex-induced heat transfer enhancement. In contrast, the teardrop-shaped dimples effectively suppressed heat transfer both upstream and downstream. The smooth tail geometry facilitated flow reattachment, reducing vortex formation and wall temperature rise. These results demonstrate the potential of teardrop-shaped dimples as a strategy for reducing cooling losses in diesel engine combustion chambers.
Shimizu et al. (Wed,) studied this question.